The Curious Case of a Castle in the Xfile
by xfilesgurl
Summary: A story about what would happen if Mulder and Scully had gone to New York and met Castle and Beckett. Set after I Want to Believe and during Season 3 of Castle.
1. Chapter 1

**Hey! so this is a crossover between the X files and Castle. Set in season 3 of Castle and after I want to Believe. Hope you enjoy! Comments are always welcome!**

**Disclaimer: I sadly do not own either the X-files or Castle but I love both of them!  
**

"Scully! Scully! Scully!" Mulder raced into the study of his house as Scully looked up from the novel she was reading.

"Mulder" she said nonchalantly.

Mulder was disappointed by her lack of enthusiasm. It was hard to surprise a woman after you'd been partners for such a long time.

"Scully I just heard from on old buddy of mine that one of their colleagues…Are you listening?"

Scully had begun reading her novel again and evidently was not paying attention to Mulder's ramblings.

Mulder shook his head and sat down on the couch opposite to the chair Scully was sitting in. "Scully" he started again. She looked up, noticing his serious look and closed her book and set it on the table next to her.

"You have my undivided attention," she said. "The adventures of Nikki Heat can wait"

Mulder smirked at the mention of Richard Castle's novel. "That's what I want to talk to you about!"

Scully looked confused. "You want to discuss Nikki Heat? Did aliens come down and pull her out of her book? Is she out on the streets trying to hunt crime but no one knows who she is and everyone keeps telling her that she's a fictional character? Do we have to find the aliens so that she can go back to Jameson Rook?"

Mulder laughed "No Scully! I meant the author." He smiled, "Richard Castle works with the NYPD right?"

Scully sat up in her chair a little more. "So I've heard."

"Well one of my buddies heard that they had an alien encounter!"

Scully sighed as she picked up her book "So Mulder? They don't work on the X-files. They are not searching for extraterrestrial answers. They should just leave it will enough alone or one of them will end up on trial from the military."

"Scully don't you see that's my point!"

Scully closed her book and once again set it on the table next to her.

"We have to stop them looking into this alien stuff. I mean I don't regret a single things we did together Scully" Mulder looked into her beautiful eyes and she smiled "If we hadn't done everything we did we wouldn't be here and we wouldn't be together." He paused "But I don't wish what we've been through on anyone. Which is why we have to go to New York and help them out."

Scully sat and stared at Mulder as she thought about everything he had just told her. Yes, their lives had been hard and yes, she wouldn't trade it for anything because it brought her to Mulder but at the same time he was right not wanting their lives to happen to other people. But what were they going to do? Go down to New York and steal the case out from under them?

"We're gonna take the case from them" Mulder announced.

Scully chuckled. She knew Mulder too well. Her face became serious "How Mulder? We don't have any ties to the FBI anymore remember? And besides I have work in the morning."

"Ya but didn't you just say that you had some vacation days coming up? We could take our old badges, dress up nice, no one in New York knows who we are. Who's going to question us? No one ever expects someone to impersonate the FBI."

Scully groaned but had no response. She wasn't sure she wanted to plunge down into the sewers again. They were getting too old for these kinds of shenanigans. But there was an allure to going out on the hunt again. She did enjoy watching Mulder become so committed to a cause. She couldn't help but want to go with him. She would always follow him no matter how ridiculous the plan.

Scully began to nod "Alright Mulder, if you think we can pull this off I'll come with you. But only for this one case. W' re not making our lives a crusade again, we're too old for that, we've given up too much to start over."

Mulder smiled and reached into his back pocket to pick out to small rectangular pieces of paper. He handed one to Scully as he kissed her cheek. She looked down at the plane ticket that was now in her hand. She chuckled.

"We leave tomorrow morning!" Mulder smiled.


	2. Chapter 2

**Chapter 2! Hope you enjoy! Comments are always welcome!**

**Disclaimer: I do not own Castle or the X-Files but I love them :)**

Scully and Mulder arrived at the 12th precinct early two days later. Both had their old FBI badges ready.

As they took the elevator up Scully said, "Mulder, what's your plan? This doesn't look like a case the FBI would intervene in."

"Don't worry Scully, I've always got a plan" Mulder winked at her as they walked out of the elevator and stared out into the busy precinct. "So who do you think is the Captain?"

"Beckett" Castle leaned over to his partner who was leaned over her desk attempting to fill out paperwork. "What Castle" Kate asked not looking up.

"Who are those people in Montgomery's office? CIA?" Castle whispered excitedly. "Castle, why would the CIA be here?" Kate said still not averting her eyes from her work. "Maybe they are a special branch of the CIA" Castle continues, "You know like men in black!" he lowered his voice and got closer the Kate's ear "You know… because of the aliens"

Kate finally looked up at Castle "There is no such thing as aliens!" "That's what they want you to think" Castle winked at her and she rolled her eyes at him and turned her focus back to her paperwork.

A few minutes later Montgomery came out of his office with a red-haired woman and a tall, lanky man. "Detective Beckett" he said as he made his way to her desk.

"Sir?" she said as she put her pen down and looked up.

"This is Agent Mulder and Agent Scully" he motioned to the two people standing next to him. "They will be assisting you on your case." The man leaned over and whispered to the woman and she shot him a warning glance.

"Why" Beckett asked confused. Castle coughed "CIA" and it was Beckett's turn to give Castle a warning glance.

"It seems that the FBI has some interest in your case." The captain looked over at the two FBI agents waiting for them to give an explanation.

"It resembles a case we had a few years ago" Mulder said.

"You once had a case where someone died from explosive decompression?" Beckett raised her eyebrow suspiciously.

"Yes" Mulder said simply.

"Okay, glad that's settled, get to work people" the captain walked back into his office.

"Okay so what have we got so far?" Mulder asked.

Beckett sighed and explained how they had found a machine that could cause the death of the woman but the machine had relinquished no evidence so they ruled out that it had been used as the murder weapon and were looking elsewhere for possible explanations or perhaps a similar machine. Agent Scully seemed to be paying no attention to what Beckett was saying but Mulder kept nodding as she spoke. When she finished explaining he told her that he and his partner were going to go chase some leads of their own.

"I don't like this Castle" Beckett whispered when the two FBI agents had left.

"Come on Kate, its cool. We're working with the FBI," Castle's voice raised in excitement.

"It's not the first time we've worked with the FBI Castle" Kate groaned,

"Hey" Esposito walked over to Kate's desk, "Who was the couple of spiffy looking people that were just hear?"

"FBI agents" Castle said giddily. "That's what I thought" Esposito said thoughtfully, "They look like those two agents that used to hunt the paranormal."

Beckett raised her eyebrows "The paranormal?"

"Ya" Esposito continued, "My buddy's dad was in the FBI at the time and he used to tell stories about the crazy cases they would investigate. The guy was obsessed with aliens."

Beckett hit Castle's arm and turned to him, "That's why they're here! They're hunting aliens!"

"Haha!" Castle smiled, "I knew there were aliens!"

"None of their cases were ever proven to be true." Esposito said, "Most people just think they're crazy. I'd watch my back if I were you."

"Will do Espo" Kate said wondering what she was going to do about the strange situation they had gotten into.

"So Mulder, still think there are aliens?" Scully asked as they got ready for bed in a small motel on the outskirts of the city.

"You never know Scully. It's better to be safe than sorry" Mulder pulled down the comforter and hopped into the old twin sized bed.

Scully rolled her eyes, "But they have so much evidence suggesting against it Mulder. I mean they found a machine that was most likely used as the murder weapon," she hopped into bed next to him, squirming as she tried to get comfortable in the tiny bed.

"Ya but they didn't find any evidence in the machine. I'm not ready to leave just yet" Mulder leaned over and turned off the light that was on the nightstand next to him.

"Alright Mulder but I think we should tread carefully, the woman doesn't seem very happy to have us there." She too leaned over to turn off the lamp on her side.

"Ya but the man seemed excited about it" Mulder said.

"He's a writer, what do you expect?" Scully said.

"I don't know, I like em" "Of course you do" Scully rolled her eyes and gently kissed Mulder's lips, "Goodnight" she said. "Goodnight" he smiled.


End file.
